Aircraft flight deck instrument panels typically include integral lighting systems to illuminate the panel nomenclature and markings on displays and controls located on the panels. The integral lighting systems generally assist a flight crew in locating displays and controls while operating the aircraft. Accordingly, the flight deck illumination systems include panel lighting and associated control systems that provide illumination for various panels and further permits the light intensity of various lighting sources positioned on the panels to be controlled. Other flight deck lighting systems include master dim and test (MD&T) systems that are operable to control a lighting level on one or more flight deck annunciators (that may have more that a single lighting level, such as a “bright” and a “dim” setting), and to further provide illumination tests for the one or more flight deck annunciators. In the present context, a flight deck annunciator is understood to include an illumination source that is not ordinarily illuminated during normal flight operations, and which is activated upon the detection of a predetermined fault or alarm condition in an associated system. Other panel lighting systems may optionally include a Master Brightness Control System, that is operable to override all flight deck panel back lighting levels, while still allowing minor localized adjustments to be made by use of the local lighting zone controls.
FIG. 1 is a block diagrammatic view of a panel lighting system 10 according to the prior art. The system 10 includes a plurality of lighted panels 12 that further include one or more illumination sources 14. The lighted panels 12 are coupled to an electrical energy source 16 through one or more dimmer control units (DCU) 18. Each DCU 18 is operable to convert a voltage and/or current received from the source 16 (e.g., 115 volts, AC) to a suitable voltage and/or current for the illumination sources 14 located in the lighted panels 12 (e.g., 5 volts AC), and to provide other necessary control functions. A desired illumination level on the lighted panels 12 is controlled by adjusting a control potentiometer 20 that is coupled to the DCU's 18. Although the foregoing panel lighting system 10 is generally effective to achieve a desired level of illumination from the sources 14, drawbacks nevertheless exist. For example, numerous DCU's 18 are generally required, which undesirably increases the weight and expense of the aircraft. In addition, if the foregoing Master Brightness Control System feature is included in the system 10, complicated analog circuitry is generally installed between the control potentiometers 20 and DCU 18, which also adds weight and expense to the aircraft. Still further, electrical conductors that couple the DCU's 18 to respective panels 12 generally vary in length, which undesirably contributes to non-uniform illumination of the panels 12 due to voltage drops occurring along the conductors. Accordingly, considerable redesign and/or rework efforts may be required to balance the voltage drops so that a relatively uniform panel illumination level is achieved.
FIG. 2 is a block diagrammatic view of a master dim and test (MD&T) system 30 according to the prior art. The system 30 includes a plurality of annunciator panels 32 that include one or more illuminated annunciators 34. The annunciator panels 32 are coupled to a suitable electrical energy source 36 through a plurality of master dim and test (MD&T) cards 38 that are generally positioned within a MD&T card file 40. The MD&T cards 38 are configured to provide lighting power (which may be variable if the system 30 is configured to permit bright and dim levels to be selected) to selected annunciators 34 so they may activate at a desired illumination level upon receiving an appropriate actuating signal from an associated system. As noted above, the MD&T system 30 also provides test capability for all annunciators located on the flight deck. Accordingly, the MD&T cards 38 generally include various logic circuits that are responsive to the actuating signal, and further include logic circuits to suitably control various test modes for each of the annunciator panels 32. Although the foregoing system 30 suitably provides the power, logic and illumination control for the panels 32, a principal drawback associated with the system 30 is that the MD&T cards 38 may be incorrectly installed within the MD&T card file 40 so that a desired dim and/or test function is not achieved. Furthermore, a failure in a single card or even a single annunciator within a circuit may result in the improper activation of multiple annunciators, since control is typically achieved using various switches and logic to provide a circuit path to ground. The MDT card file 40 also undesirably occupies a significant volume within the aircraft and adds considerable weight and cost to the aircraft.
It would therefore be desirable to have flight deck panel illumination systems that occupy less volume and are generally lighter and less expensive than present flight deck panel illumination systems. Furthermore, it would be desirable to have flight deck panel illumination systems that substantially avoid rework and reconfiguration of the systems in order to achieve relatively uniform illumination levels in illumination sources positioned on the flight deck panel.